Check if user is authenticated with Ruby on Rails Devise

Im using Rails 4 and Devise 3

I am overwriting the sessions controller. For creating a session, I would like to check if user is confirmed first or not, but I'm not sure how to check if the user is confirmed. This is what I would like to do:

sessions controller

def create
    if USER_CONFIRMED?? 
        return render :json => {:success => false, :type => "signin", :errors => ["You have to confirm your email address before continuing."]}
    else
        resource = warden.authenticate!(:scope => resource_name, :recall => "#{controller_path}#failure")
        sign_in_and_redirect(resource_name, resource)
    end
end

Thank you.